Stirling Engine Exhaust Casing Integration for Turbomachine Power Generation
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Solution Overview
Problem
The generation of electricity in turbofan engines is penalized by the need for mechanical power from high-pressure compressors, which reduces engine performance, and existing solutions like Stirling cycle engines are not suitable for aeronautical use due to size and weight constraints.
Innovation Solution
A dual-flow turbomachine integrating a Stirling cycle heat engine with two heat exchangers and a regenerator, utilizing the temperature difference between exhaust gases and cold air to generate electrical energy, minimizing weight and size increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If an electromechanical generator driven by power take-off from high-pressure compressors is used, then electricity generation is achieved, but engine performance is penalized due to mechanical power loss
Solution Approach 1:
The invention converts the harmful waste heat from exhaust gases into useful electrical energy through a Stirling engine. The exhaust heat, which would otherwise be wasted, drives the Stirling cycle to generate electricity, transforming a negative factor (heat loss) into a positive benefit (power generation) without affecting the primary engine's mechanical output
Solution Approach 2:
The invention replaces the traditional electromechanical generator driven by mechanical power take-off with a thermal engine (Stirling engine) that directly converts thermal energy from exhaust gases into mechanical work, which then drives an electrical generator. This substitution eliminates the need to extract mechanical power from the compressor, preserving engine performance
2Use of energy by moving object
If a Stirling cycle engine is used for electricity generation, then thermal energy from exhaust gases can be utilized, but the machine is heavy and large in size making it unsuitable for aeronautical use
Solution Approach 1:
The Stirling engine components are nested within the exhaust casing structure of the turbojet engine. The heat exchangers are integrated into the radial arms of the exhaust casing, and the working chamber is positioned within the available space in the exhaust flow path. This nesting approach allows the Stirling engine to utilize the existing structural space without adding significant external volume or weight to the overall engine assembly
Solution Approach 2:
The exhaust casing radial arms serve dual functions: providing structural support for the exhaust flow and housing the heat exchangers of the Stirling engine. The exhaust casing structure is thus multi-functional, simultaneously managing exhaust flow and enabling thermal energy conversion, which reduces the need for additional dedicated components and minimizes overall weight
3Loss of energy
If a Stirling cycle engine is integrated into the turbomachine, then electricity generation from exhaust heat is achieved, but the size of the Stirling engine and associated means increases
Solution Approach 1:
The heat exchangers are arranged radially within the exhaust casing arms, utilizing the radial dimension of the exhaust flow path. The working chamber is positioned at the radially inner end of the radial arm, inside the inner cylindrical wall. This three-dimensional spatial arrangement within the exhaust casing volume allows compact integration of all Stirling engine components without extending the overall engine envelope
Solution Approach 2:
The heating and cooling exchangers are connected by a regenerator housed in a part of the radial arm located between the flow paths of the primary and secondary flows. The regenerator serves as both a thermal energy storage device and a structural connector between exchangers, merging multiple functions into a single integrated component that reduces overall system volume
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution allows for efficient electricity generation from thermal energy in exhaust gases without drawing mechanical power from the turbomachine, improving turbojet engine performance and reducing specific consumption by approximately 1%.
Implementation Method 1
a first heat exchanger for heating, by the primary flow, a working fluid
Implementation Method 2
a first heat exchanger for heating, by the primary flow, a working fluid
Implementation Method 3
a second heat exchanger for cooling the working fluid by the secondary flow
Implementation Method 4
a second heat exchanger for cooling the working fluid by the secondary flow
Implementation Method 5
a regenerator intended to accumulate thermal energy during the cooling phase of the Stirling cycle and to release thermal energy during the heating phase
Implementation Method 6
at least one heat engine operating according to a Stirling cycle comprising two exchangers for heating and cooling respectively of a working fluid
Implementation Method 7
the mechanical energy thus obtained being capable of being converted into electrical energy
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
Turbomachine comprising at least one Stirling cycle heat engine which is mounted at the end of a radial arm (36) of the exhaust casing (24) and includes a working chamber (40) located outside the primary (B) and secondary (A) flows, a displacing piston (42) associated with a moving element (44) of a power generation system, and two heat exchangers, heating (58) and cooling (62), formed in parts of the radial arm intercepting respectively the primary flow (B) and the secondary flow (A), these two heat exchangers (58, 62) communicating with each other and with the working chamber (40) for the circulation of a working fluid.